Field of the Invention
The present invention relates to a solid oxide fuel cell stack, and more particularly to a solid oxide fuel cell stack that can expand both in the vertical and horizontal directions and use simple flow channel design to reach a uniform flow distribution.
Description of the Prior Art
Generally speaking, solid oxide fuel cell (SOFC) can be classified into two types, including a tube SOFC and a planar SOFC, according to its shape. In order to raise the powering voltage of the system it is applied to, one approach is to serially connect a plurality of fuel cells to increase its output voltage. Since the planar SOFCs can be stacked and serially connected in a much more costless and spaceless way compared to tube SOFCs, they are mostly widely used in the recent markets nowadays.
Based on different processes, solid oxide fuel cells can also be classified into four kinds, including an electrolyte-supported SOFC, an anode-supported SOFC, a cathode-supported SOFC and a metal-supported SOFC. The electrolyte-supported SOFC was mainly utilized in the past to solve the problems that fuel stack may crack easily, however, there were still issues relating to the electrolyte-supported SOFCs due to its high operating temperature which is usually around 1000K˜1100K. In order to decrease the operating temperature, one approach is to cut down the thickness of the electrolyte in the fuel stack. Therefore, so far as production cost and complexity of the production itself are concerned, the anode-supported SOFC are gradually used to replace the rest three kinds of SOFCs. In general, the anode-supported SOFC can have the best powering efficiency when its cathode thickness equals to 20 μm. Nevertheless, it should be noticed that when the cathode thickness is 20 μm, it is way too thin for a solid oxide fuel cell. When it is involving with a traditional interconnect which has linear flow channels, it affects the diffusion of the oxygen thereby reducing its power efficiency since an area that the interconnect covers and is exposed to the cathode of the fuel stack is too large.
Moreover, the gas flow itself also has great impact on the powering efficiency of the fuel cell. Several prior arts provide different ways which relate to varying the width of the flow channel to make the gas flow uniform. However, these designs are still too complicated. For example, although a cross-flow pattern can provide a simpler flow channel design, when it is applied to the SOFC, the fuel cell has the problems of low powering efficiency and large temperature difference inside the cell.
Besides, when the system involves with a plurality of SOFCs, these conventional fuel cells can only be connected in a serial direction, which needs to increase the area of the cell module or to use a great number of serially-connected cell modules. However, increasing the area of the cell module replies on much more advanced technology. More serially-connected cell modules affect the uniformity of the gas flowing into the interconnect, thereby having great impact on the temperature and voltage distribution of the system and reducing its operating life-time. Moreover, when employing a plurality of cell modules, it increases both the complexity and cost of the system.
On account of above, it should be obvious that there is indeed an urgent need for the professionals in the field for a new solid oxide fuel cell stack to be developed that can effectively reach a uniform gas distribution flowing into its interconnect, meanwhile maintain its high powering efficiency and solve the temperature difference problem occurring in the prior design.